The present invention relates generally to an intrinsically safe device and, more specifically, an intrinsically safe module for conveying signals to or from a field device located in a hazardous area.
The National Electrical Code mandates that wiring and devices used in a hazardous environment be intrinsically safe in that they are incapable of releasing electrical or thermal energy to cause ignition of a volatile gas or gaseous mixture. In general, an intrinsically safe environment has a safe side and a hazardous side. Not only the device located on the hazardous side must meet the intrinsically safe requirements, but the associated apparatus located on the safe side and electronically linked to the device located on the hazardous side must also be intrinsically safe.
In an intrinsically safe application, it is a common practice to use an intrinsically safe barrier as a safety buffer between a device located on the hazardous side and an apparatus located on the safe side. For example, when a thermocouple is placed in a hazardous area to measure a temperature, the thermocouple is connected to an associated temperature reading apparatus via an intrinsically safe barrier. Both the associated temperature reading apparatus and the intrinsically safe barrier are placed in the safe area. The thermocouple, in this usage, and other devices that are used on the hazardous side of an intrinsically safe environment are commonly referred to as field devices.
Field devices are classified as simple or complex. Simple devices are electrical or electro-mechanical elements that either do not store energy or do not generate more than 1.2 volts, 0.1 amps, 25 mW or 20 femto-Joules. For example, contacts, switches (pressure, flow and level), strain gages, thermocouples, resistance temperature devices (RTDs), light-emitting diodes (LEDs) and resistors are classified as simple field devices. Complex devices may store excess energy capable of causing ignition of a volatile atmospheric mixture. For example, electrical transmitters, solenoids, relays and transducers are classified as complex field devices. Among the above-mentioned electrical and electro-mechanical components, contacts, transmitters and temperature sensors are the most commonly used field devices in intrinsically safe applications.
Transmitters are commonly referred to as analog inputs. They are used to convert a physical measurement such as temperature or pressure into an electrical signal in the 4-20 mA current range to be sent from a hazardous area to a safe area. In the safe area, a signal processor is used to receive the electrical signals and to convert the electrical signals into a temperature or pressure reading. Typically, a transmitter is powered by 24 VDC.
Different field devices may operate at different current ranges and voltage levels. For example, a field device such as an LED is typically rated at 24, 18, 12 or 6 VDC and operates at about 25 mA. Other field devices may operate at a 0-20 mA or 0-25 mA current range.
What type of signal processor is to be used to convey signals to or from a field device depends on the nature of the field device. For example, if the field device is a variable speed rotary valve, then the signal processor must be capable of supplying a current level within a certain current range to vary the valve speed. Thus, when a user uses a field device, he or she must be able to select a signal processor that is capable of handling the current range or voltage level required by the field device. Furthermore, the user must connect one or more intrinsically safe barriers between the field device and the signal processor in order to meet the intrinsic safety requirements. Furthermore, the user may be required to use an intrinsically safe or regulated power supply to provide field power to the field device. The cost incurred to the user in order to meet the intrinsic safety requirements is usually high, and the selection of a suitable signal processor and safety barrier can be very time-consuming.
Therefore, it is advantageous and desirable to provide an intrinsically safe, integrated module such that the user can simply connect the field device to the integrated module without worrying about matching the electrical requirements of the field device.
It is an object of the present invention to provide an intrinsically safe integrated module containing a signal processor with a plurality of I/O connectors to allow a user to use a field device in an intrinsically safe environment.
It is another object of the present invention to provide an intrinsically safe, integrated module wherein the signal processor and the I/O connectors are configurable to handle different current ranges and/or voltage levels.
The integrated module of the present invention comprises:
a plurality of first intrinsically safe barriers;
a signal processor having a plurality of I/O connectors for conveying signals to or from one or more field devices through the first intrinsically safe barriers;
a second intrinsically safe barrier; and
a power supply to provide electrical power to the field device through the second intrinsically safe barrier.
Preferably, the second intrinsically safe barrier comprises a Zener barrier while the first intrinsically safe barrier can be a Zener barrier or a galvanic isolation barrier.
Preferably, the I/O connectors include at least one input connector and one current output connector so that the input and output connectors form a current loop together with the field device.
Preferably, each I/O connector is software-configurable so that it can handle a plurality of current ranges.
Preferably, each I/O connector is software-configurable so that it can handle a plurality of voltage levels.
The present invention will become apparent upon reading the description taken in conjunction with FIGS. 1-4.